Whilst your MEMART would contain general provisions with regard to the object of the company and its corporate governance structure, a Shareholders Agreement goes further to govern the relationship among the shareholders, and between the shareholders and the company itself.
A standard shareholders agreement would have clauses relating to the disposal or transfer of shares such as pre-emptive rights, rights of first refusal, redemption of shares upon death or disability among others. It would also include other clauses such as issues requiring shareholder approval, assignment of IP and invention rights to the company, appointment of directors etc.